Generation of Col2a1-EGFP iPS cells for monitoring chondrogenic differentiation

Dynamic enhancer landscapes in human craniofacial development

The genetic basis of human facial variation and craniofacial birth defects remains poorly understood. Distant-acting transcriptional enhancers control the fine-tuned spatiotemporal expression of genes during critical stages of craniofacial development. However, a lack of accurate maps of the genomic locations and cell type-resolved activities of craniofacial enhancers prevents their systematic exploration in human genetics studies. Here, we combine histone modification, chromatin accessibility, and gene expression profiling of human craniofacial development with single-cell analyses of the developing mouse face to define the regulatory landscape of facial development at tissue- and single cell-resolution. We provide temporal activity profiles for 14,000 human developmental craniofacial enhancers. We find that 56% of human craniofacial enhancers share chromatin accessibility in the mouse and we provide cell population- and embryonic stage-resolved predictions of their in vivo activity. Taken together, our data provide an expansive resource for genetic and developmental studies of human craniofacial development.

Cell Type- and Tissue-specific Enhancers in Craniofacial Development

The genetic basis of craniofacial birth defects and general variation in human facial shape remains poorly understood. Distant-acting transcriptional enhancers are a major category of non-coding genome function and have been shown to control the fine-tuned spatiotemporal expression of genes during critical stages of craniofacial development1-3. However, a lack of accurate maps of the genomic location and cell type-specific in vivo activities of all craniofacial enhancers prevents their systematic exploration in human genetics studies. Here, we combined histone modification and chromatin accessibility profiling from different stages of human craniofacial development with single-cell analyses of the developing mouse face to create a comprehensive catalogue of the regulatory landscape of facial development at tissue- and single cell-resolution. In total, we identified approximately 14,000 enhancers across seven developmental stages from weeks 4 through 8 of human embryonic face development. We used transgenic mouse reporter assays to determine the in vivo activity patterns of human face enhancers predicted from these data. Across 16 in vivo validated human enhancers, we observed a rich diversity of craniofacial subregions in which these enhancers are active in vivo. To annotate the cell type specificities of human-mouse conserved enhancers, we performed single-cell RNA-seq and single-nucleus ATAC-seq of mouse craniofacial tissues from embryonic days e11.5 to e15.5. By integrating these data across species, we find that the majority (56%) of human craniofacial enhancers are functionally conserved in mice, providing cell type- and embryonic stage-resolved predictions of their in vivo activity profiles. Using retrospective analysis of known craniofacial enhancers in combination with single cell-resolved transgenic reporter assays, we demonstrate the utility of these data for predicting the in vivo cell type specificity of enhancers. Taken together, our data provide an expansive resource for genetic and developmental studies of human craniofacial development.

Enhanced chondrogenic differentiation of iPS cell-derived mesenchymal stem/stromal cells via neural crest cell induction for hyaline cartilage repair

Background: To date, there is no effective long-lasting treatment for cartilage tissue repair. Primary chondrocytes and mesenchymal stem/stromal cells are the most commonly used cell sources in regenerative medicine. However, both cell types have limitations, such as dedifferentiation, donor morbidity, and limited expansion. Here, we report a stepwise differentiation method to generate matrix-rich cartilage spheroids from induced pluripotent stem cell-derived mesenchymal stem/stromal cells (iMSCs) via the induction of neural crest cells under xeno-free conditions. Methods: The genes and signaling pathways regulating the chondrogenic susceptibility of iMSCs generated under different conditions were studied. Enhanced chondrogenic differentiation was achieved using a combination of growth factors and small-molecule inducers. Results: We demonstrated that the use of a thienoindazole derivative, TD-198946, synergistically improves chondrogenesis in iMSCs. The proposed strategy produced controlled-size spheroids and increased cartilage extracellular matrix production with no signs of dedifferentiation, fibrotic cartilage formation, or hypertrophy in vivo. Conclusion: These findings provide a novel cell source for stem cell-based cartilage repair. Furthermore, since chondrogenic spheroids have the potential to fuse within a few days, they can be used as building blocks for biofabrication of larger cartilage tissues using technologies such as the Kenzan Bioprinting method.

Induction of iPSC-derived Prg4-positive cells with characteristics of superficial zone chondrocytes and fibroblast-like synovial cells

Background

Lubricin, a proteoglycan encoded by the PRG4 gene, is synthesised by superficial zone (SFZ) chondrocytes and synovial cells. It reduces friction between joints and allows smooth sliding of tendons. Although lubricin has been shown to be effective against osteoarthritis and synovitis in animals, its clinical application remains untested. In this study, we aimed to induce lubricin-expressing cells from pluripotent stem cells (iPSCs) and applied them locally via cell transplantation.

Methods

To generate iPSCs, OCT3/4, SOX2, KLF4, and L-MYC were transduced into fibroblasts derived from Prg4-mRFP1 transgenic mice. We established a protocol for the differentiation of iPSC-derived Prg4-mRFP1-positive cells and characterised their mRNA expression profile. Finally, we injected Prg4-mRFP1-positive cells into the paratenon, surrounding the Achilles tendons and knee joints of severe combined immunodeficient mice and assessed lubricin expression.

Result

Wnt3a, activin A, TGF-β1, and bFGF were applied to induce the differentiation of iPSC-derived Prg4-mRFP1-positive cells. Markers related to SFZ chondrocytes and fibroblast-like synovial cells (FLSs) were expressed during differentiation. RNA-sequencing indicated that iPSC-derived Prg4-mRFP1-positive cells manifested expression profiles typical of SFZ chondrocytes and FLSs. Transplanted iPSC-derived Prg4-mRFP1-positive cells survived around the Achilles tendons and in knee joints.

Conclusions

The present study describes a protocol for the differentiation of iPSC-derived Prg4-positive cells with characteristics of SFZ chondrocytes and FLSs. Transplantation of lubricin-expressing cells offers promise as a therapy against arthritis and synovitis.

Developmental principles informing human pluripotent stem cell differentiation to cartilage and bone

Human pluripotent stem cells can differentiate into any cell type given appropriate signals and hence have been used to research early human development of many tissues and diseases. Here, we review the major biological factors that regulate cartilage and bone development through the three main routes of neural crest, lateral plate mesoderm and paraxial mesoderm. We examine how these routes have been used in differentiation protocols that replicate skeletal development using human pluripotent stem cells and how these methods have been refined and improved over time. Finally, we discuss how pluripotent stem cells can be employed to understand human skeletal genetic diseases with a developmental origin and phenotype, and how developmental protocols have been applied to gain a better understanding of these conditions.

Oct4 facilitates chondrogenic differentiation of mesenchymal stem cells by mediating CIP2A expression

Bone development and cartilage formation require strict modulation of gene expression for mesenchymal stem cells (MSCs) to progress through their differentiation stages. Octamer-binding transcription factor 4 (Oct4) expression is generally restricted to developing embryonic pluripotent cells, but its role in chondrogenic differentiation (CD) of MSCs remains unclear. We therefore investigated the role of Oct4 in CD using a microarray, quantitative real-time polymerase chain reaction, and western blotting. The expression of Oct4 was elevated when the CD of cultured MSCs was induced. Silencing Oct4 damaged MSC growth and proliferation and decreased CD, indicated by decreased cartilage matrix formation and the expression of Col2a1, Col10a1, Acan, and Sox9. We found a positive correlation between the expression of CIP2A, a natural inhibitor of protein phosphatase 2A (PP2A) and that of Oct4. Cellular inhibitor of PP2A (CIP2A) expression gradually increased after CD. Overexpression of CIP2A in MSCs with Oct4 depletion promoted cartilage matrix deposition as well as Col2a1, Col10a1, Acan, and Sox9 expression. The chondrogenic induction triggered c-Myc, Akt, ERK, and MEK phosphorylation and upregulated c-Myc and mTOR expression, which was downregulated upon Oct4 knockdown and restored by CIP2A overexpression. These findings indicated that Oct4 functions as an essential chondrogenesis regulator, partly via the CIP2A/PP2A pathway.

Evidence that TD-198946 enhances the chondrogenic potential of human synovium-derived stem cells through the NOTCH3 signaling pathway

Human synovium-derived stem cells (hSSCs) are an attractive source of cells for cartilage repair. At present, the quality of tissue and techniques used for cartilage regeneration have scope for improvement. A small compound, TD-198946, was reported to enhance chondrogenic induction from hSSCs; however, other applications of TD-198946, such as priming the cell potential of hSSCs, remain unknown. Our study aimed to examine the effect of TD-198946 pretreatment on hSSCs. HSSCs were cultured with or without TD-198946 for 7 days during expansion culture and then converted into a three-dimensional pellet culture supplemented with bone morphogenetic protein-2 (BMP2) and/or transforming growth factor beta-3 (TGFβ3). Chondrogenesis in cultures was assessed based on the GAG content, histology, and expression levels of chondrogenic marker genes. Cell pellets derived from TD-198946-pretreated hSSCs showed enhanced chondrogenic potential when chondrogenesis was induced by both BMP2 and TGFβ3. Moreover, cartilaginous tissue was efficiently generated from TD-198946-pretreated hSSCs using a combination of BMP2 and TGFβ3. Microarray analysis revealed that NOTCH pathway-related genes and their target genes were significantly upregulated in TD-198946-treated hSSCs, although TD-198946 alone did not upregulate chondrogenesis related markers. The administration of the NOTCH signal inhibitor diminished the effect of TD-198946. Thus, TD-198946 enhances the chondrogenic potential of hSSCs via the NOTCH3 signaling pathway. This study is the first to demonstrate the gradual activation of NOTCH3 signaling during chondrogenesis in hSSCs. The priming of NOTCH3 using TD-198946 provides a novel insight regarding the regulation of the differentiation of hSSCs into chondrocytes.

A lithium-containing biomaterial promotes chondrogenic differentiation of induced pluripotent stem cells with reducing hypertrophy

Background

Induced pluripotent stem cells (iPSCs) exhibit limitless pluripotent plasticity and proliferation capability to provide an abundant cell source for tissue regenerative medicine. Thus, inducing iPSCs toward a specific differentiation direction is an important scientific question. Traditionally, iPSCs have been induced to chondrocytes with the help of some small molecules within 21–36 days. To speed up the differentiation of iPSCs, we supposed to utilize bioactive ceramics to assist chondrogenic-induction process.

Methods

In this study, we applied ionic products (3.125~12.5 mg/mL) of the lithium-containing bioceramic (Li₂Ca₄Si₄O₁₃, L2C4S4) and individual Li⁺ (5.78~23.73 mg/L) in the direct chondrogenic differentiation of human iPSCs.

Results

Compared to pure chondrogenic medium and extracts of tricalcium phosphate (TCP), the extracts of L2C4S4 at a certain concentration range (3.125~12.5 mg/mL) significantly enhanced chondrogenic proteins Type II Collagen (COL II)/Aggrecan/ SRY-Box 9 (SOX9) synthesis and reduced hypertrophic protein type X collagen (COL X)/matrix metallopeptidase 13 (MMP13) production in iPSCs-derived chondrocytes within 14 days, suggesting that these newly generated chondrocytes exhibited favorable chondrocytes characteristics and maintained a low-hypertrophy state. Further studies demonstrated that the individual Li⁺ ions at the concentration range of 5.78~23.73 mg/L also accelerated the chondrogenic differentiation of iPSCs, indicating that Li⁺ ions played a pivotal role in chondrogenic differentiation process.

Conclusions

These findings indicated that lithium-containing bioceramic with bioactive specific ionic components may be used for a promising platform for inducing iPSCs toward chondrogenic differentiation and cartilage regeneration.

Single-Cell RNA Sequencing of Human Embryonic Stem Cell Differentiation Delineates Adverse Effects of Nicotine on Embryonic Development

Nicotine, the main chemical constituent of tobacco, is highly detrimental to the developing fetus by increasing the risk of gestational complications and organ disorders. The effects of nicotine on human embryonic development and related mechanisms, however, remain poorly understood. Here, we performed single-cell RNA sequencing (scRNA-seq) of human embryonic stem cell (hESC)-derived embryoid body (EB) in the presence or absence of nicotine. Nicotine-induced lineage-specific responses and dysregulated cell-to-cell communication in EBs, shedding light on the adverse effects of nicotine on human embryonic development. In addition, nicotine reduced cell viability, increased reactive oxygen species (ROS), and altered cell cycling in EBs. Abnormal Ca2+ signaling was found in muscle cells upon nicotine exposure, as verified in hESC-derived cardiomyocytes. Consequently, our scRNA-seq data suggest direct adverse effects of nicotine on hESC differentiation at the single-cell level and offer a new method for evaluating drug and environmental toxicity on human embryonic development in utero.

Step-Wise Chondrogenesis of Human Induced Pluripotent Stem Cells and Purification Via a Reporter Allele Generated by CRISPR-Cas9 Genome Editing

The differentiation of human induced pluripotent stem cells (hiPSCs) to prescribed cell fates enables the engineering of patient-specific tissue types, such as hyaline cartilage, for applications in regenerative medicine, disease modeling, and drug screening. In many cases, however, these differentiation approaches are poorly controlled and generate heterogeneous cell populations. Here, we demonstrate cartilaginous matrix production in three unique hiPSC lines using a robust and reproducible differentiation protocol. To purify chondroprogenitors (CPs) produced by this protocol, we engineered a COL2A1-GFP knock-in reporter hiPSC line by CRISPR-Cas9 genome editing. Purified CPs demonstrated an improved chondrogenic capacity compared with unselected populations. The ability to enrich for CPs and generate homogenous matrix without contaminating cell types will be essential for regenerative and disease modeling applications. Stem Cells 2019;37:65-76.

2 dyn/cm2 shear force upregulates kruppel-like factor 4 expression in human chondrocytes to inhibit the interleukin-1β-activated nuclear factor-κB

The shear force effect on human chondrocytes is time and magnitude dependent. Recently, kruppel-like factor (KLF) 4 has been identified as a pleiotropic protein and its activity in cells is dependent on different stimuli and/or cell types. The role of KLF4 in chondrocytes is still unclear and there has been no report determining whether shear force regulates KLF4 levels in chondrocytes. Hence, this study was carried out to investigate the role of KLF4 in human chondrocytes under shear force stimulation and the underlying mechanism. Human primary and SW1353 chondrocytes were used in this study. The shear forces at 2, 5, or 15 dyn/cm² intensity were applied to both types of human chondrocytes. The specific small interfering RNAs, activators, and inhibitors were used to study the detailed mechanism of shear force. The presented results showed that 2, but not 5 and 15, dyn/cm² shear force increases KLF4 expression in human primary and SW1353 chondrocytes. Extracellular signal-regulated kinase 5 induced peroxisome proliferator-activated receptor γ transcription activity to increase KLF4 transcription. Moreover, the KLF4 induction in human chondrocytes in response to 2 dyn/cm² shear force could attenuate interleukin (IL)-1β-stimulated nuclear factor-κB activation. These results elucidate the role of KLF4 in antagonizing the effect of IL-1β in human chondrocytes under 2 dyn/cm² shear force stimulation and provide a possible mechanism to demonstrate the protection of moderate forces or exercises in cartilage.

Repair potential of nonsurgically delivered induced pluripotent stem cell-derived chondrocytes in a rat osteochondral defect model

Human induced pluripotent stem cells (hiPSCs) are thought to be an alternative cell source for future regenerative medicine. hiPSCs may allow unlimited production of cell types that have low turnover rates and are difficult to obtain such as autologous chondrocytes. In this study, we generated hiPSC-derived chondrogenic pellets, and chondrocytes were isolated. To confirm the curative effects, chondrogenic pellets and isolated chondrocytes were transplanted into rat joints with osteochondral defects. Isolated hiPSC-derived chondrocytes were delivered in the defect by a single intra-articular injection. The generated hiPSC-derived chondrogenic pellets had increased chondrogenic marker expression and accumulated extracellular matrix proteins. Chondrocytes were successfully isolated from the pellets. Alcian blue staining and collagen type II were detected in the cells. Chondrogenic marker expression was also increased in the isolated cells. Transplanted chondrogenic pellets and chondrocytes both had curative effects in the osteochondral defect rat model. Detection of human proteins in the joints proved that the cells were successfully delivered into the defect. Chondrogenic pellets or chondrocytes generated from hiPSCs have potential as regenerative medicine for cartilage recovery or regeneration. Chondrocytes isolated from hiPSC-derived chondrogenic pellets had curative effects in damaged cartilage. Injectable hiPSC-derived chondrocytes show the possibility of noninvasive delivery of regenerative medicine for cartilage recovery.

Isolation and biological characteristic evaluation of a novel type of cartilage stem/progenitor cell derived from Small‑tailed Han sheep embryos

Cartilage stem/progenitor cells (CSPCs) are a novel stem cell population and function as promising therapeutic candidates for cell‑based cartilage repair. Until now, numerous existing research materials have been obtained from humans, horses, cows and other mammals, but rarely from sheep. In the present study, CSPCs with potential applications in repairing tissue damage and cell‑based therapy were isolated from 45‑day‑old Small‑tailed Han Sheep embryos, and examined at the cellular and molecular level. The expression level of characteristic surface markers of the fetal sheep CSPCs were also evaluated by immunofluorescence, reverse transcription‑polymerase chain reaction analysis and flow cytometric assays. Biological growth curves were drawn in accordance with cell numbers. Additionally, karyotype analysis showed no marked differences in the in vitro cultured CSPCs and they were genetically stable among different passages. The CSPCs were also capable of adipogenic, osteogenic and chondrogenic lineage progression under the appropriate induction medium in vitro. Together, these findings provide a theoretical basis and experimental evidence for cellular transplant therapy in tissue engineering.

Combating Osteoarthritis through Stem Cell Therapies by Rejuvenating Cartilage: A Review

Knee osteoarthritis (OA) is a chronic degenerative disorder which could be distinguished by erosion of articular cartilage, pain, stiffness, and crepitus. Not only aging-associated alterations but also the metabolic factors such as hyperglycemia, dyslipidemia, and obesity affect articular tissues and may initiate or exacerbate the OA. The poor self-healing ability of articular cartilage due to limited regeneration in chondrocytes further adversely affects the osteoarthritic microenvironment. Traditional and current surgical treatment procedures for OA are limited and incapable to reverse the damage of articular cartilage. To overcome these limitations, cell-based therapies are currently being employed to repair and regenerate the structure and function of articular tissues. These therapies not only depend upon source and type of stem cells but also on environmental conditions, growth factors, and chemical and mechanical stimuli. Recently, the pluripotent and various multipotent mesenchymal stem cells have been employed for OA therapy, due to their differentiation potential towards chondrogenic lineage. Additionally, the stem cells have also been supplemented with growth factors to achieve higher healing response in osteoarthritic cartilage. In this review, we summarized the current status of stem cell therapies in OA pathophysiology and also highlighted the potential areas of further research needed in regenerative medicine.

Orthopedic tissue regeneration: cells, scaffolds, and small molecules

Orthopedic tissue regeneration would benefit the aging population or patients with degenerative bone and cartilage diseases, especially osteoporosis and osteoarthritis. Despite progress in surgical and pharmacological interventions, new regenerative approaches are needed to meet the challenge of creating bone and articular cartilage tissues that are not only structurally sound but also functional, primarily to maintain mechanical integrity in their high load-bearing environments. In this review, we discuss new advances made in exploiting the three classes of materials in bone and cartilage regenerative medicine--cells, biomaterial-based scaffolds, and small molecules--and their successes and challenges reported in the clinic. In particular, the focus will be on the development of tissue-engineered bone and cartilage ex vivo by combining stem cells with biomaterials, providing appropriate structural, compositional, and mechanical cues to restore damaged tissue function. In addition, using small molecules to locally promote regeneration will be discussed, with potential approaches that combine bone and cartilage targeted therapeutics for the orthopedic-related disease, especially osteoporosis and osteoarthritis.

Repair of cartilage defects in osteoarthritis rats with induced pluripotent stem cell derived chondrocytes

Background

The incapacity of articular cartilage (AC) for self-repair after damage ultimately leads to the development of osteoarthritis. Stem cell-based therapy has been proposed for the treatment of osteoarthritis (OA) and induced pluripotent stem cells (iPSCs) are becoming a promising stem cell source.

Results

Three steps were developed to differentiate human iPSCs into chondrocytes which were transplanted into rat OA models induced by monosodium iodoacetate (MIA). After 6 days embryonic body (EB) formation and 2 weeks differentiation, the gene and protein expression of Col2A1, GAG and Sox9 has significantly increased compare to undifferentiated hiPSCs. After 15 weeks transplantation, no immune responses were observed, micro-CT showed gradual engraftment and the improvement of subchondrol plate integrity, and histological examinations demonstrated articular cartilage matrix production.

Conclusions

hiPSC could be an efficient and clinically translatable approach for cartilage tissue regeneration in OA cartilages.

Stem Cells in Skeletal Tissue Engineering: Technologies and Models

This review surveys the use of pluripotent and multipotent stem cells in skeletal tissue engineering. Specific emphasis is focused on evaluating the function and activities of these cells in the context of development in vivo, and how technologies and methods of stem cell-based tissue engineering for stem cells must draw inspiration from developmental biology. Information on the embryonic origin and in vivo differentiation of skeletal tissues is first reviewed, to shed light on the persistence and activities of adult stem cells that remain in skeletal tissues after embryogenesis. Next, the development and differentiation of pluripotent stem cells is discussed, and some of their advantages and disadvantages in the context of tissue engineering are presented. The final section highlights current use of multipotent adult mesenchymal stem cells, reviewing their origin, differentiation capacity, and potential applications to tissue engineering.

Hyaline cartilage formation and tumorigenesis of implanted tissues derived from human induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) are a promising cell source for cartilage regenerative medicine. Meanwhile, the risk of tumorigenesis should be considered in the clinical application of human iPSCs (hiPSCs). Here, we report in vitro chondrogenic differentiation of hiPSCs and maturation of the differentiated hiPSCs through transplantation into mouse knee joints. Three hiPSC clones showed efficient chondrogenic differentiation using an established protocol for human embryonic stem cells. The differentiated hiPSCs formed hyaline cartilage tissues at 8 weeks after transplantation into the articular cartilage of NOD/SCID mouse knee joints. Although tumors were not observed during the 8 weeks after transplantation, an immature teratoma had developed in one mouse at 16 weeks. In conclusion, hiPSCs are a potent cell source for regeneration of hyaline articular cartilage. However, the risk of tumorigenesis should be managed for clinical application in the future.

Isolation, identification and differentiation of human embryonic cartilage stem cells

We isolated human embryonic cartilage stem cells (hECSCs), a novel stem cell population, from the articular cartilage of eight-week-old human embryos. These stem cells demonstrated a marker expression pattern and differentiation potential intermediate to those of human embryonic stem cells (hESCs) and human adult stem cells (hASCs). hECSCs expressed markers associated with both hESCs (OCT4, NANOG, SOX2, SSEA-3 and SSEA-4) and human adult stem cells (hASCs) (CD29, CD44, CD90, CD73 and CD10). These cells also differentiated into adipocytes, osteoblasts, chondrocytes, neurons and islet-like cells under specific inducing conditions. We identified N(6), 2'-O-dibutyryl cyclic adenosine 3':5'-monophosphate (Bt2cAMP) as an inducer of chondrogenic differentiation in hECSCs. Similar results using N(6), 2'-O-dibutyryl cyclic adenosine 3':5'-monophosphate (Bt2cAMP) were obtained for two other types of human embryonic tissue-derived stem cells, human embryonic hepatic stem cells (hEHSCs) and human embryonic amniotic fluid stem cells (hEASCs), both of which exhibited a marker expression pattern similar to that of hECSCs. The isolation of hECSCs and the discovery that N(6), 2'-O-dibutyryl cyclic adenosine 3':5'-monophosphate (Bt2cAMP) induces chondrogenic differentiation in different stem cell populations might aid the development of strategies in tissue engineering and cartilage repair.